In general, where were the muslim states of africa established?

One of the main ways that Islam spread into Africa was through trade. The people of the Arabian Peninsula were skilled traders, being connected to international trade for generations. Some of these routes stretched as far as China. The east coast of Africa was already full of powerfultrading cities, urban kingdoms with economies that were almost completely dependent on export and trade. Their success was largely geographic. Sitting at the intersection of the Red and Arabian Seas gave them access to maritime routes to India and China, and their proximity to the Mediterranean Sea connected them to the trade networks of the Middle East and Europe.